Acromegaly is characterized by growth hormone(GH) hypersecretion from a pituitary somatotroph tumor. The mechanism(s) of pituitary tumorigenesis are unknown. To look at the possibility that hypothalamic growth hormone releasing hormone(GHRH) is important in the pathogenesis of acromegaly, we propose to study 10 acromegalic subjects who will be having surgery for removal of their pituitary tumor. Subjects will be admitted to the GCRC for 10 days. They will be given a continuous infusion of GHRH antagonist for 7 days. Numerous tests will be done before and after the GHRH bolus dose, and response to thyrotropin releasing hormone (TRH) bolus dose. In addition, part of the pituitary tumor removed during the operation will be retained by investigators for further in-vitro tests. This study will implicate (or exclude) hypothalamic GHRH as a promoter of somatrotroph adenomatous transformation and hyperfunction.